The present invention relates broadly to gaskets for providing electromagnetic interference (EMI) shielding and weather, dust, or other environmental sealing, and particularly to a combination or composite gasket construction and method of its manufacture combining a metal mesh strip gasket with an integral solid or foam elastomeric weather-sealing strip which is especially adapted for use within cabinets and other enclosures for electrical or electronic systems or devices.
The operation of electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed xe2x80x9celectromagnetic interferencexe2x80x9d or xe2x80x9cEMIxe2x80x9d as being known to interfere with the operation of other proximate electronic devices.
To attenuate EMI effects, shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other xe2x80x9ctargetxe2x80x9d devices from other source devices. Such shielding is provided as a barrier which is inserted between the source and the other devices, and typically is configured as an electrically conductive and grounded housing which encloses the device. As the circuitry of the device generally must remain accessible for servicing or the like, most housings are provided with openable or removable accesses such as doors, hatches, panels, or covers. Between even the flattest of these accesses and its corresponding mating or faying surface, however, there may be present gaps which reduce the efficiency of the shielding by presenting openings through which radiant energy may leak or otherwise pass into or out of the device. Moreover, such gaps represent discontinuities in the surface and ground conductivity of the housing or other shielding, and may even generate a secondary source of EMI radiation by functioning as a form of slot antenna. In this regard, bulk or surface currents induced within the housing develop voltage gradients across any interface gaps in the shielding, which gaps thereby function as antennas which radiate EMI noise. In general, the amplitude of the noise is proportional to the gap length, with the width of the gap having less appreciable effect.
For filling gaps within mating surfaces of housings and other EMI shielding structures, gaskets and other seals have been proposed both for maintaining electrical continuity across the structure, and for excluding from the interior of the device such contaminates as moisture and dust. Such seals are bonded or mechanically attached to, or press-fit into, one of the mating surfaces, and function to close any interface gaps to establish a continuous conductive path thereacross by conforming under an applied pressure to irregularities between the surfaces. Accordingly, seals intended for EMI shielding applications are specified to be of a construction which not only provides electrical surface conductivity even while under compression, but which also has a resiliency allowing the seals to conform to the size of the gap. The seals additionally must be wear resistant, economical to manufacture, and capability of withstanding repeated compression and relaxation cycles. EMI shielding gaskets and other electrically-conductive materials, their methods of manufacture, and their use are further described in U.S. Pat. Nos. 6,121,545; 6,096,413; 6,075,205; 5,996,220; 5,910,524; 5,902,956; 5,902,438; 5,882,729; 5,804,762; 5,731,541; 5,641,438; 5,603,514; 5,584,983; 5,578,790; 5,566,055; 5,524,908; 5,522,602; 5,512,709; 5,438,423; 5,294,270; 5,202,536; 5,142,101; 5,141,770; 5,136,359; 5,115,104; 5,107,070; 5,105,056; 5,068,493; 5,054,635; 5,049,085; 5,028,739; 5,008,485; 4,988,550; 4,979,280; 4,968,854; 4,952,448; 4,931,479; 4,931,326; 4,871,477; 4,864,076; 4,857,668; 4,800,126; 4,529,257; 4,441,726; 4,301,040; 4,231,901; 4,065,138; 3,758,123; 3,026,367; 2,974,183; and 2,755,079, in U.S. patent appln. Publ. No. 20020010223, International (PCT) Patent Appln. Nos. WO 01/71223; 01/54467; 00/23,513; 99/44,406; 98/54942; 96/22672; and 93/23226, Japanese Patent Publication (Kokai) No. 7177/1993, European Pat. Appln. No. 1,094,257, German Patent No. 19728839, and Canadian Patent No. 903,020, in Severinsen, J., xe2x80x9cGaskets That Block EMI,xe2x80x9d Machine Design, Vol. 47, No. 19, pp. 74-77 (Aug. 7, 1975), and in the following publications of the Chomerics Division of Parker Hannifin Corporation, Woburn, Mass.: xe2x80x9cSOFT-SHIELD(copyright) 1000 Series;xe2x80x9d xe2x80x9cSOFT-SHIELD(copyright) 2000 Series;xe2x80x9d xe2x80x9cSOFT-SHIELD(copyright) 4000 Series;xe2x80x9d xe2x80x9cSOFT-SHIELD(copyright) 5000 Series;xe2x80x9d and xe2x80x9cSOFT-SHIELD(copyright) 5500, Preliminary Product Data Sheet (1998) Series; xe2x80x9cCOMBO(copyright) STRIP Gaskets;xe2x80x9d xe2x80x9cSPRINGMESH(trademark) Highly Resilient EMI Mesh Gasket,xe2x80x9d Technical Bulletin 114; xe2x80x9cMETAL STRIP(copyright) All Metal Gaskets;xe2x80x9d xe2x80x9cSHIELDMESH(trademark) Compressed Mesh Gaskets;xe2x80x9d and xe2x80x9cMETALKLIP(copyright) Clip-On EMI Gasket.xe2x80x9d
EMI shielding gaskets typically are constructed as a resilient element, or a combination of one or more resilient elements having gap-filling capabilities. One or more of the elements may be provided as a tubular or solid, foamed or unfoamed core or strip which is filled, sheathed, or coated to be electrically-conductive, or otherwise which is formed of an inherently conductive material such as a metal wire spring mesh. One or more of the other elements, and particularly in the case of a composite or xe2x80x9ccombination gasketxe2x80x9d having a conductive EMI shielding element in combination with an integral weather sealing strip (such as is sold commercially by the Chomerics Division of Parker-Hannifin Corporation (Woburn, Mass.) under the name xe2x80x9cCOMBO(copyright) STRIP Gasketxe2x80x9d), may be formed of a sheet, strip, xe2x80x9cpicture-frame,xe2x80x9d or other open or closed geometry of a solid, i.e., unfoamed, or foamed elastomeric material providing enhanced environmental sealing capabilities to which the conductive element is adhesively-bonded or otherwise joined. Each of the core or strip of the conductive element and the elastomeric material of the environmental sealing element may be formed of an elastomeric thermoplastic material such as polyethylene, polypropylene, or polyvinyl chloride, a thermoplastic or thermosetting rubber such as a butadiene, styrene-butadiene, nitrile, chlorosulfonate, neoprene, urethane, or silicone, or a blend such as polypropylene-EPDM. Conductive materials for the filler, sheathing, or coating of the conductive element include metal or metal-plated particles, fabrics, meshes, and fibers. Preferred metals include copper, nickel, silver, aluminum, tin or an alloy such as Monel, with preferred fibers and fabrics including natural or synthetic fibers such as cotton, wool, silk, cellulose, polyester, polyamide, nylon, polyimide. Alternatively, other conductive particles and fibers such as carbon, graphite, or a conductive polymer material may be substituted.
Conventional manufacturing processes for EMI shielding gaskets include extrusion, molding, or die-cutting, with molding or die-cutting heretofore being preferred for particularly small or complex shielding configurations. In this regard, die-cutting involves the forming of the gasket from a cured sheet of an electrically-conductive elastomer which is cut or stamped using a die or the like into the desired configuration. Molding, in turn, involves the compression or injection molding of an uncured or thermoplastic elastomer into the desired configuration.
More recently, a form-in-place (FIP) process has been proposed for the manufacture of EMI shielding gaskets. As is described in commonly-assigned U.S. Pat. Nos. 6,096,413; 5,910,524; 5,641,438; 4,931,479, and International (PCT) Patent Appln. No. 96/22672; and in U.S. Pat. Nos. 5,882,729 and 5,731,541, International (PCT) Patent Appln. No. WO 01/71223, and Japanese Patent Publication (Kokai) No. 7177/1993, such process involves the application of a bead of a viscous, curable, electrically-conductive composition which is dispensed in a fluent state from a nozzle directly onto to a surface of a substrate such as a housing or other enclosure. The composition, typically a silver-filled or otherwise electrically-conductive silicone or polyurethane foamed or unfoamed elastomer, then is foamed and/or cured-in-place via a chemical, thermal, or physical reaction which may be initiated or catalyzed via the application of heat or with atmospheric moisture or ultraviolet (UV) radiation to form an electrically-conductive, elastomeric EMI shielding gasket profile in situ on the substrate surface. By forming and curing the gasket in place directly on the substrate surface, the need for separate forming and installation steps is obviated. Moreover, the gasket may be adhered directly to the surface of the substrate to further obviate the need for a separate adhesive component or other means of attachment of the gasket to the substrate. In contrast to more conventional die cutting or molding processes, the flashless FIP process reduces waste generation, and additionally is less labor intensive in that the need for hand assembly of complex gasket shapes or the mounting of the gasket into place is obviated. The process further is amenable to an automated or robotically-controlled operation, and may be employed to fabricate complex gasket geometries under atmospheric pressure and without the use of a mold.
As electronic devices continue to proliferate, it is believed that additional EMI shielding products and methods of manufacture therefor would be well-received by the electronics industry.
The present invention is directed to a combination EMI shielding and environmental sealing gasket construction and method of manufacturing the same which is especially adapted for use in xe2x80x9cpicture-framexe2x80x9d and complex geometric configurations and/or in applications requiring a high level of weather or other environmental sealing such as in outdoor cabinets. The gasket construction includes one or more electrically-conductive EMI shielding gasket members, each of which may be a mesh, spring mesh, or an elastomeric or foam core covered in a mesh, and one or more integral environmental sealing members which may be robotically dispensed or otherwise formed-in-place around the shielding members as formed of a foamed or unfoamed elastomer.
In an illustrative embodiment, the one or more shielding gasket members may be provided as a resilient strip of a mesh or spring mesh which may have a generally circular, oval, xe2x80x9cD,xe2x80x9d polygonal, or other shape cross-section and which may be preformed by conventional methods into the geometry, which may be a closed geometric shape such as a circle, square, rectangle, or other xe2x80x9cpicture framexe2x80x9d-like shape, of the cabinet door or other structure, equipment, or device to be sealed.
Alternatively, the shielding gasket members may be provided as individual strips. In whatever form provided, the members may be placed, typically in a spaced-apart arrangement in the case of two or more members, in a grooved formed into a mold or other tool or, alternatively, directly into the cabinet, door, access panel, housing, or other structure to be sealed, such groove having a width which is sized relative to the widthwise extents of the members to define a predefined clearance therebetween corresponding to the desired widthwise extent of the sealing member which is to be formed. With the one or more shielding members being received in the groove, a form-in-place (FIP) gasket material may be dispensed, such as from a nozzle which may be robotically-controlled or by other automated means, within the groove along at least a portion of one or both sides of at least one of the shielding gasket members. With the dispensed material being foamed or otherwise expanding or flowing within the groove, the material thus is made to penetrate through the open spaces or interstices of the mesh and into at least a portion of the widthwise dimension of the shielding gasket member.
Upon the curing of the material, one or both of the shielding gasket members are at least partially embedded within the material which otherwise forms one or more environment sealing members, typically having a D-shaped profile characteristic of formed-in-place seals, between the shielding gasket members and/or between such members and the side walls of the groove. Optionally, the free surface of the sealing gasket being formed may be contained within a by a molding plate or other forming tool so as to effect the forming of the sealing gasket into a different profile such as a square or rectangle. Advantageously, by virtue of the penetration of the sealing material into the interstices of the mesh, the shielding and sealing gasket members are thereby mechanically and/or, depending upon the composition of the sealing material, which may be a polyurethane or silicone foam, adhesively or otherwise chemically bonded to form an integral combination gasket structure, with the need to bond the members together using a separate adhesive layer or otherwise in a separate joining operation being obviated.
The combination of the gasket of the invention may be produced in frames, sheets strips, or other forms which may be mounted to the structure to be sealed. Alternatively, the gasket construction may be formed-in-placed directly on the structure to be sealed.
The present invention, accordingly, comprises the articles and methods of manufacture possessing the construction, combination of elements, and arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantageously, the gasket construction and form-in-place method of the present invention facilitate the net shape manufacture of picture-frame and other complex shapes or patterns of any dimension and which may include internal openings with less waste as compared, for example, to a die-cut part. Such construction and method, moreover, are amenable to the use of automated processing equipment and obviate the need for splicing and other operations which conventionally are preformed by hand. Thus, the gasket construction and method of the invention are particularly reliable and economical, and may be used in a variety of configurations, such as sheets, strips, pads, picture-frames, and die-cut-like patterns, in thin or thick cross-sections, and in a host of shielding and/or grounding applications such as for door or access panels, vents, and covers of cabinets and other enclosures. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.